Tone Stack Idea (need help)

[Casey4s]

I am bored to death with the usual tone stacks in guitar amps so I have been trying to find something better.  My first attempt wound up with 15 triode sections. It got way out of control so I started over with this one.  I tried to add midrange but I am pretty sure I just have two levels of Bass instead.  I can tweak the values if I can come up with solid architecture in the first place.

Does anyone have any helpful thoughts or suggestions to add a midrange?  I might bump the treble to .0056 and 500pf to get a better starting point.

Thanx...

[Tiny_Daddy]

Check out the tone control arrangements in Bell &  Howell Film-O-Sound amps for something really different.

[Dave]

I've played thru some old Sound City amps that had active tone controls.

Dave

[Casey4s]

Check out the tone control arrangements in Bell &  Howell Film-O-Sound amps for something really different.

 I can't find a schematic but I am looking. 

Thanks

[stingray_65]

Ted Weber offers up this design, 1 tube active TMB.

"This is an active tone control. In other words, it is a tone stack with gain. A dual triode and all other parts are included in the kit. Using an active tone stack will give you a lot more range on the bass, mids, and treble control." from Weber's VST web site.

https://taweber.powweb.com/store/tca_schem.jpg

I think I would consider using an AT7 less gain, but I think it may offer a wider frequency response.

I've been wanting to build this a few years now, just never got to it.

Ray

[stingray_65]

I am bored to death with the usual tone stacks in guitar amps so I have been trying to find something better.  My first attempt wound up with 15 triode sections. It got way out of control so I started over with this one.  I tried to add midrange but I am pretty sure I just have two levels of Bass instead.  I can tweak the values if I can come up with solid architecture in the first place.

Does anyone have any helpful thoughts or suggestions to add a midrange?  I might bump the treble to .0056 and 500pf to get a better starting point.

Thanx...

Re read the original post.

I think the design you've put forth looks great.

I would be tempted to leave out the mid control and keep the design in 1 tube. But I like that Fender mid range scoop.

To compensate, add a presence circuit to the NFB if you have one

Just some late nite thoughts.
Ray

[PRR]

The "mid" pot appears to be a bass control scaled lower than your "bass" pot.

The general action is as boring as a James, but more complicated/costly.

You have gain of ~~125 (50*0.1*50*0.1*50*0.1) and you propose putting where you normally have gain of 0.1.... seems like 1000:1 too much gain.

Why is the fist stage driven from a cathode follower? The grid impedance is near infinite. Actually you gonna need a C and R, so the grid is maybe 1Meg, still no need for CF. In 5F6-A the CF is preceded by a gain-of-25 stage. You could omit both these stages and only have 40:1 excess gain.

The bass and treble can be combined in one network: the very common "James" tone control.

You can add a midrange control but the results suck. You want to keep it separate.

All of these simple plans are "boring".

For real zing you want narrower peaks/dips targeted at guitar sounds.

This is all just frequency shaping. You can't frequency-shape a soprano into a baritone or a saxophone.

Get a clean booster/buffer and a hifi or studio graphic EQ. Learn what the frequency bands do boost/cut. Then design just the useful changes into a simpler plan.

> amps that had active tone controls.

Active or passive isn't really the question. The tube/transistor/chip has infinite flat response; all tone action is resistors and caps (and coils). Some complicated plans work better "active". But any frequency shape may be arrived at with purely passive methods.

[PRR]

> consider using an AT7 less gain, but I think it may offer a wider frequency response.

It's fed-back to unity-gain (with knobs centered).

Optimized for 12AX7 "unity" is 0.98; with 12AT7 gives 0.97. No change.

Maximum boost will be somewhat less with 12AT7; but there's other problems.

Assuming a source which can drive a load falling below 10K at the top of the band (a real "if") the bandwidth is FAR past the audio band either way.

The network is "perfect" with an infinite gain amplifier. With bypassed 12AX7 it can get within 2dB of 20dB boost, which is good; but this plan omits the cathode bypass.

The cathode follower is severely starved for plate-cathode drop. It looks like the 5F6-A stage but the cathode resistor is mis-copied. It distorts; apparently bad enough that another 20K was thrown under the CF to soften the hash. Change 1.5K to 820 (Fender's value) or even 470. (The 12AT7 would bias better, but that's dartboard design.)

There's serious interaction between Treb and Mid.

It really wants a CF ahead of it.

Try it. Weber did have a good ear. It may be flawed in "good" ways. And you can't kick about the cost.

[jjasilli]

Does this stuff help?:  http://dogstar.dantimax.dk/tubestuf/dzart-6.htm

http://www.ultimate-guitar.com/forum/showthread.php?t=952137

[Casey4s]

To everyone who replied ... thank you .. thank you... thank you.


I have gained a lot from this infromation. I am going to try the Weber idea and see how that works out.



About the cathode follower; it's only mentioned because in the 5f6A type circuit the CF is there. I will probably eliminate the CF if I am in pahse going into the PI.


The basic idea in the beginning is an "enhanced" stack for a 5F6 build.  I am doing a bunch of other simple mods just for fun, like post PI master, revoiced inputs, a boost stage, switchable SS & Tube rectification, and switchable Cathode or Foxed bias, and reverb.   I realize this is a lot of silly "fluff" but what the heck, it will be a lot of fun and a test bed so to speak.

"There really are no failed amps... just prototypes in progress"